Various electro-optical systems have been developed for reading optical indicia, such as bar codes. A bar code is a coded pattern of graphical indicia comprised of a series of bars and spaces of varying widths, the bars and spaces having differing light reflecting characteristics. Systems that read and decode bar codes employing CCD or CMOS-based imaging systems are typically referred to as imaging-based bar code readers or bar code scanners.
The imaging bar code reader includes an imaging and decoding system including an imaging system for generating an image of a target bar code and decoding circuitry for decoding the imaged target bar code. Imaging systems include CCD arrays, CMOS arrays, or other imaging pixel arrays having a plurality of photosensitive elements or pixels. Light reflected from a target image, e.g., a target bar code is focused through a lens of the imaging system onto the pixel array. Output signals from the pixels of the pixel array are digitized by an analog-to-digital converter. Decoding circuitry of the imaging and decoding system processes the digitized signals and attempts to decode the imaged bar code.
Many modern imaging systems include a computing device that interfaces with video data. This interface is usually accomplished using a direct-memory-access (DMA) method or through a special hardware interface, such as a video port, that is part of the processor of the computing device. The object of these two approaches is to allow the computing device to process a relatively large amount of video data without overloading the computing bandwidth of the processor or the data access bandwidth of the memory bus.
Some imaging systems are designed to process data from more than one camera. Other systems process data from one or more cameras as well as packets of data about, for example, the video image being processed that has been computed by a co-processor. Some examples of co-processors include FPGA, ASICs, and DSPs. The use of co-processors allows the imaging system to be designed with relatively simple and inexpensive microprocessors.
While cost effective, inexpensive microprocessors tend to have limited bandwidth interfaces to external devices. These microprocessors usually include a video port that is a high bandwidth interface that is configured to accept data in a digital video format. In the digital video format the data is organized in a contiguous block, thus allowing the processor to accept all data with minimum effort in handshaking, even if the data is transmitted in multiple, discontinuous transmission sessions. Allowing discontinuous video transmission frees up the processor bandwidth to access and process data between these sessions, while at the same time reducing the amount of data that the sending component must buffer.
In imaging systems with multiple systems or additional data to be processed, the overhead involved in switching between the different data destinations may be so high that the use of an inexpensive microprocessor is not feasible.